Lubricating oil compositions comprising fischer-tropsch derived base oils

ABSTRACT

Use of a lubricating oil composition comprising at least one Fischer-Tropsch derived base oil for reducing exhaust port blocking of a 2-stroke engine. The present invention also relates to a 2-stroke lubricating engine oil composition comprising (i) at least one Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. in the range of from 2 to 30 mm 2 /s at 100° C. and (ii) 5 wt % or greater of a hydrocarbon solvent; wherein the lubricating engine oil composition has a Blocking Index of greater than 130 as measured by the JASO M343-92 Exhaust System Blocking Test Method.

FIELD OF THE INVENTION

The present invention relates to the use of a lubricating oilcomposition comprising a Fischer-Tropsch derived base oil for reducingexhaust port blocking of a two-stroke engine and to a two-strokelubricating engine oil composition having reduced exhaust port blocking.

BACKGROUND OF THE INVENTION

Two-stroke gasoline engines are used in motorcycles as well as in gardenand recreational equipment such as lawn mowers, chain saws, stringtrimmers, mopeds, snow-mobiles, outboard marine motors and the like.Slow speed two-stroke diesel engines are used for marine propulsion invery large ships.

To operate a two-stroke gasoline engine the crankcase holds a mixture oftwo-stroke gasoline lubricant and fuel and the crankcase serves as apressurization chamber to force air/fuel into the cylinder. Thisnecessitates the use of a lubricating composition which has beenspecially formulated for two-stroke engines, instead of a high viscositylubricating oil such as those used in 4-stroke engines. The 2-strokeengine lubricant is mixed with gasoline in prescribed proportions tolubricate the crankshaft, connecting rod and cylinder walls.

Conventional two-stroke gasoline engine lubricants are typicallyformulated with a mineral oil base oil or synthetic base oil and alow-viscosity, low-boiling hydrocarbon solvent to enhance themiscibility of the lubricant with the gasoline.

Some two-stroke engine oils have used ester base oils with no lowboiling solvent to reduce flammability and minimize smoky emissions.However these lubricants often suffer from poor oxidation stability.Other two-stroke engine oils have used polyalphaolefin base oils havingimproved low temperature properties. Both PAOs and ester base oilssuffer from the disadvantage of being limited in supply and veryexpensive.

A variety of performance additives can be added to improve the overallperformance of the lubricant. In particular, a two-stroke engine oilshould meet the requirements set by standards setting organizations,including Japanese Automobile Standard JASO M345 2003 and InternationalStandard ISO 1373832000(E).

Since conventional two-stroke engines tend to be rather smoky,smoke-reducing additives are often added to the lubricant. Examples ofsmoke-reducing additives include those that contain metals, but thesetend to be undesirable from an environmental viewpoint. Other examplesinclude synthetic basestocks, but these tend to be expensive.Polybutenes and polyisobutylenes are also commonly added for reducingsmoke and as anti-scuffing agents. It is taught in WO2007/050352 thatpolyisobutylenes contribute to exhaust port deposits and clogging.

It would be desirable to provide a lubricating oil composition which issuitable for use in a two-stroke engine oil and which, in particular,provides improvements in exhaust port blocking behaviour.

At the same time, it would also be desirable to provide a 2-strokelubricating oil composition which exhibits reduced engine wear, reducedpollution, good low-temperature performance, good gasoline miscibility,high oxidation stability, high flash points, and which meets therequirements of standard setting organizations such as JapaneseAutomobile Standard JASO M345 2003 and International Standard ISO1373832000(E).

It has now surprisingly been found that by using a Fischer-Tropschderived base oil, preferably a heavy

Fischer-Tropsch derived base oil, as a base oil in a two-stroke enginelubricating oil composition, an improved two-stroke engine lubricatingoil composition is provided which exhibits, in particular, a reductionin exhaust port blocking.

SUMMARY OF THE INVENTION

According to the present invention there is provided the use of alubricating oil composition comprising at least one Fischer-Tropschderived base oil for reducing exhaust port blocking of a 2-strokeengine.

According to another aspect of the present invention there is provided a2-stroke lubricating engine oil composition comprising (i) at least oneFischer-Tropsch derived base oil having a kinematic viscosity at 100° C.in the range of from 2 to 30 mm²/s and (ii) 5 wt % or greater of ahydrocarbon solvent; wherein the lubricating engine oil composition hasa Blocking Index of greater than 130 as measured by the JASO M343-92Exhaust System Blocking Test Method.

According to yet a further aspect of the present invention there isprovided a 2-stroke lubricating engine oil composition comprising (i) afirst Fischer-Tropsch derived base oil having a kinematic viscosity at100° C. in the range of from 2 mm²/s to 10 mm²/s and (ii) a secondFischer-Tropsch derived base oil having kinematic viscosity at 100° C.in the range of from 18 mm²/s to 30 mm²/s; wherein the weight ratio ofthe first Fischer-Tropsch base oil to the second Fischer-Tropsch baseoil is in the range of from 10:1 to 1:5, and wherein the lubricatingengine oil composition has a Blocking Index of greater than 130 asmeasured by the JASO M343-92 Exhaust System Blocking Test Method.

It has surprisingly been found that the use of Fischer-Tropsch derivedbase oil, preferably heavy Fischer-Tropsch derived base oil, in the2-stroke lubricating oil compositions herein provides reduced exhaustport blocking.

The use of a Fischer-Tropsch derived base oil allows replacement ofpolyisobutylenes on a viscometric basis.

It is to be expected that the same benefit would be manifest in a2-stroke diesel engine, especially a 2-stroke slow speed marine dieselengine.

The 2-stroke lubricating oil compositions according to the presentinvention also provide reduced engine wear, increased lubricity, reducedpollution, an improved smoke index, good low-temperature performance,satisfactory gasoline miscibility, high oxidation stability, high flashpoints and reduced flammability.

The 2-stroke engine oil of the present invention also meets therequirements of Japanese Automobile Standard JASO M345 2003 andInternational Standard ISO 1373832000(E).

DETAILED DESCRIPTION OF THE INVENTION

The 2-stroke lubricating oil composition for use herein comprises atleast one Fischer-Tropsch derived base oil.

Fischer-Tropsch derived base oils are known in the art. By the term“Fischer-Tropsch derived” is meant that a base oil is, or is derivedfrom, a synthesis product of a Fischer-Tropsch process. AFischer-Tropsch derived base oil may also be referred to as a GTL(Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oilsthat may be conveniently used as the base oil in the lubricatingcomposition are those as for example disclosed in EP 0 776 959, EP 0 668342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO01/57166.

The Fischer-Tropsch derived base oil preferably has a kinematicviscosity at 100° C. in the range of from 2 mm²/s to 30 mm²/s. The totalamount of Fischer-Tropsch derived base oil in the lubricating oilcomposition is preferably in the range of from 5 wt % to 99 wt %, morepreferably from 10 wt % to 99 wt %.

In one embodiment of the present invention the lubricating oilcomposition comprises a light Fischer-Tropsch derived base oil having akinematic viscosity at 100° C. in the range of from 2 mm²/s to 10 mm²/s,preferably in the range of from 2 mm²/s to 4 mm²/s. In one embodiment,the light Fischer-Tropsch derived base oil is present at a level of from5 wt % to 60 wt %, preferably at a level of from 20 wt % to about 60 wt%.

In another embodiment of the present invention the lubricating oilcomposition comprises a heavy Fischer-Tropsch derived base oil having akinematic viscosity at 100° C. in the range of from 12 mm²/s to 30mm²/s, preferably in the range of from 18 mm²/s to 22 mm²/s. The heavyFischer-Tropsch derived base oil is preferably present at a level offrom 5 wt % to about 60 wt %, preferably from 10 wt % to 50 wt %.

In a preferred embodiment of the present invention the lubricating oilcomposition comprises a heavy Fischer-Tropsch derived base oil having akinematic viscosity at 100° C. in the range of from 12 mm²/s to 30mm²/s, preferably in the range of from 18 mm²/s to 22 mm²/s, and lessthan 2 wt % of a light Fischer-Tropsch base oil having a kinematicviscosity at 100° C. in the range of from 2 mm²/s to 10 mm²/s. In thelatter embodiment, the lubricating oil composition is preferably free oflight Fischer-Tropsch derived base oil having a kinematic viscosity at100° C. in the range of 2 mm²/s to 20 mm²/s.

In yet another embodiment of the present invention, the lubricating oilcomposition comprises a mixture of a first Fischer-Tropsch oil which isa light Fischer Tropsch base oil having a kinematic viscosity at 100° C.in the range of from 2 mm²/s to 10 mm²/s, preferably in the range offrom 2 mm²/s to 4 mm²/s, and a second Fischer-Tropsch base oil which isa heavy Fischer-Tropsch base oil having a kinematic viscosity at 100° C.in the range of from 12 mm²/s to 30 mm²/s, preferably in the range offrom 18 mm²/s to 22 mm²/s. In the latter embodiment, it is preferredthat the weight ratio of the first Fischer-Tropsch derived base oil andthe second Fischer-Tropsch derived base oil is in the range of from 10:1to 1:5, more preferably in the range of from 1.98:1 to 0.01:1.

In addition to the Fischer-Tropsch derived base oil, the lubricatingcomposition herein may comprise one or more additional base oils. Thereare no particular limitations regarding the additional base oil(s) whichcan be used in the lubricating composition of the present invention, andvarious conventional mineral oils, synthetic oils as well as naturallyderived esters such as vegetable oils may be conveniently used.

The additional base oil may conveniently comprise mixtures of one ormore mineral oils and/or one or more synthetic oils; thus, the term“base oil” may refer to a mixture containing more than one base oil orbase stock. Mineral oils include liquid petroleum oils andsolvent-treated or acid-treated mineral lubricating oil of theparaffinic, naphthenic, or mixed paraffinic/naphthenic type which may befurther refined by hydrofinishing processes and/or dewaxing.

Suitable base oils for use in the lubricating oil compositions hereinare Group I-III mineral base oils, Group IV poly-alpha olefins (PAOs),and Group V base oils.

By “Group I”, “Group II”, “Group III” “Group IV” and “Group V” base oilsare meant lubricating oil base oils according to the definitions ofAmerican Petroleum Institute (API) for categories I-V. These APIcategories are defined in API Publication 1509, 16th Edition, AppendixE, April, 2007.

Synthetic oils include hydrocarbon oils such as olefin oligomers(including polyalphaolefin base oils; PAOs), dibasic acid esters, polyolesters, polyalkylene glycols (PAGs), alkyl naphthalenes and dewaxed waxyisomerates. API Group III hydrocarbon base oils sold by the Shell Groupunder the designation “Shell XHVI” (trade mark) may be convenientlyused.

Poly-alpha olefin base oils (PAOs) and their manufacture are well knownin the art. Preferred poly-alpha olefin base oils that may be used inthe lubricating compositions may be derived from linear C₂ to C₃₂,preferably C₆ to C₁₆, alpha olefins. Particularly preferred feedstocksfor said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and1-tetradecene.

The total amount of base oil incorporated in the lubricating compositionis preferably present in an amount in the range of from 60 to 99 wt. %,more preferably in an amount in the range of from 65 to 98 wt. % andmost preferably in an amount in the range of from 70 to 95 wt. %, withrespect to the total weight of the lubricating composition.

Preferably, the finished lubricating composition has a kinematicviscosity in the range of from 2 to 30 mm²/s at 100 ° C., morepreferably in the range of from 3 to 20 mm²/s, most preferably in therange of from 4 to 15 mm²/s.

Preferably, the lubricating oil composition comprises 5 wt % or greaterof a volatile hydrocarbon solvent. The inclusion of such a solvent isfor the purpose of improving the miscibility and/or solubility of baseoil and additives with gasoline or other fuel.

Preferably the volatile hydrocarbon solvent is present in thecomposition at a level in the range of 5 to 40 wt %, preferably in therange of 10 wt % to 30 wt %, more preferably in the range of from 20 wt% to 30 wt %, by weight of the total composition.

Examples of suitable volatile hydrocarbon solvents include kerosene,Exxsol D80 commercially from Exxon Mobil Chemical Company, Shellsol D70commercially available from Shell International Chemical Company andFischer-Tropsch kerosene commercially available from Shell InternationalPetroleum Company.

Another preferred component for use in the lubricating compositionsherein is a smoke-suppression agent. In a preferred embodiment, thesmoke-suppression agent is an olefinically unsaturated polymer selectedfrom the group consisting of polybutene, polyisobutylene or a mixture ofpolybutene and polyisobutylene, which has a number average molecularweight of 400 to 2200 and a terminal olefin content of at least 60 mol%, based on the total number of double bonds in the polymer. These typesof smoke-suppression agents are taught in EP-A-1743932.

An example of a smoke-suppression agent is that commercially availablefrom BASF Corporation under the tradename Glissopal (RTM) 1000, anapproximately 1000 Dalton poly-isobutylene. Other examples would bepoly-butylenes of similar molecular weight supplied by Ineos Oligomersunder the trade name Indopol.

The smoke-suppression agent is preferably present in the composition ata level in the range of from 5% to 70%, preferably in the range of from10% to 55%, by weight of the total composition.

One or more detergent/dispersant additive packages may be included inthe lubricating oil composition of the present invention, preferably inan amount of from 1 to 25 wt %, more preferably from 3 to 20 wt %, basedon the total weight of composition. Ashless, low-ash or ash-containingadditives may be used for this purpose.

Suitable ashless additives include polyamide, alkenylsuccinimides, boricacid-modified alkenylsuccinimies, phenolic amines and succinatederivatives or combinations of any two or more such additives.

Suitable ash-containing detergent/dispersant additives include alkalineearth metal (e.g. magnesium, calcium, barium), salicylate, sulfonate,phosphonates or phenates or combinations of any two or more suchadditives.

Commercially available two-stroke lubricant detergent/dispersantadditive packages include, for example, Lubrizol 400, Lubrizol 6827,Lubrizol 6830, Lubrizol 600, Lubrizol 606, Oronite OLOA 9333, OroniteOLOA 340A, Oronite OLOA 6721 and Oronite OLOA 9357.

The lubricating composition may further comprise additional additivessuch as anti-wear additives, lubricity additives, extreme pressureagents, anti-oxidants, friction modifiers, viscosity index improvers,pour point depressants, rust or corrosion inhibitors, defoaming agentsand seal fix or seal compatibility agents.

The above-described additives may be present at a level in the range offrom 0.005% to 15%, preferably from 0.005% to 6%, by weight of thelubricating oil composition.

As the person skilled in the art is familiar with the above and otheradditives, these are not further discussed here in detail. Specificexamples of such additives are described in for example Kirk-OthmerEncyclopedia of Chemical Technology, third edition, volume 14, pages477-526.

To operate a two-stroke gasoline engine the crankcase holds a mixture oftwo-stroke gasoline lubricant and fuel. The recommended mix ratio oftwo-stroke gasoline engine lubricant and fuel are specified by theengine manufacturer. The fuels useful in two-stroke gasoline engines arewell known to those skilled in the art and usually contain a majorportion of a normally liquid fuel such as a hydrocarbonaceous petroleumdistillate fuel, e.g. spark ignition engine fuel as defined by ASTMD4814-07, or motor gasoline as defined by ASTM D439-89. Such fuels canalso contain non-hydrocarbonaceous materials such as alcohols, ethers,organo nitro compounds and the like. Examples of suitable fuels include,but are not necessarily limited to methanol, ethanol, diethyl ether,methylethyl ether, nitro methane and liquid fuels derived from vegetableand mineral sources such as corn, switch grass, alpha shale and coal.Examples of such fuel mixtures are combinations of gasoline and ethanol,diesel fuel and ether, gasoline and nitro methane, etc. The fuel ispreferably lead-free gasoline.

Two-stroke gasoline engine lubricants are typically used in admixturewith fuels in amounts of about 20 to 250 parts by weight of fuel per 1part by weight of lubricating oil, preferably in the range from 30 to100 parts by weight of fuel per 1 part by weight of lubricant.

It is important that the two-stroke lubricating oil composition of thepresent invention meets the requirements set by standards settingorganizations, including Japanese Automobile Standard JASO M345:2003 andInternational Standard ISO 1373832000 (E).

In particular, it has been found that the lubricating oil compositionsof the present invention provide an improved benefit in terms of reducedexhaust port blocking. Such a benefit can be measured by the standardtest method JASO 343-92.

In particular, in preferred embodiments, the lubricating oilcompositions of the present invention have a Blocking Index of greaterthan 130, preferably greater than 140, as measured by JASO 343-92.

The lubricating compositions may be conveniently prepared by admixingthe additives that are usually present in lubricating compositions, forexample as herein before described, with mineral and/or synthetic baseoil.

The present invention will now be described by reference to thefollowing Examples which are not intended to limit the scope of theinvention in any way.

EXAMPLES Example 1 and Comparative Example A

To determine the effect of GTL base oil on exhaust port blockingbehaviour in a two-stroke motorcycle engine, two-stroke motorcycle oilswere prepared having the formulations set out in Table 1 below. Theformulations were prepared by mixing the additives with the base oilsaccording to conventional preparation methods. To determine the effectof each composition on exhaust system port blocking the Blocking Indexfor each example was measured using the Exhaust System Blocking testmethod JASO M343-92.

The results of these tests are shown in Table 1.

TABLE 1 Comparative Example A Example 1 HVI 160B¹ 37.4 0 HVI 65² 0 33.88GTL 19³ 0 13.52 polybutylene 950⁴ 35 25 Shellsol D70B⁵ 25 25 Additivepackage⁶ 2.5 2.5 Irganox L135⁷ 0.1 0.1 Total (weight %) 100 100 Results:JASO Exhaust Port 98 176 Blocking Index (M343-92)

-   -   1. Mineral API Group I base oil commercially available from        Shell Pernis Refinery, Rotterdam    -   2. Mineral API Group I base oil commercially available from        Shell Pernis Refinery, Rotterdam    -   3. Heavy Fischer-Tropsch base stock having a kinematic viscosity        at 100° C. of 19 cSt as prepared according to U.S. Pat. No.        7,354,508.    -   4. Polybutylene having a molecular weight of 950    -   5. ShellSol D70B solvent commercially available from Shell        International Chemical Company, Rotterdam, The Netherlands    -   6. 2-stroke performance additive package commercially available        from Infineum, Milton Hill, Oxfordshire, UK containing aminic        dispersant, antioxidants (mixed hindered phenols and aminic        antioxidants), and over-based detergents from the range calcium        phenate and calcium salicylates.    -   7. Antioxidant commercially available from CIBA Speciality        Chemicals,Berne, Switzerland

Examples 2-4 and Comparative Example B

To determine the effect of GTL base oil on exhaust port blockingbehaviour in two-stroke engines, two-stroke motorcycle oils wereprepared having the formulations set out in Table 2 below. Theformulations were prepared by mixing the additives with the base oilsaccording to conventional preparation methods. Various measurements weremade on each of the engine lubricants using the test methods detailed inTable 2. The results of these tests are set out in Table 2.

TABLE 2 Comparative Example B Example 2 Example 3 Example 4 Performance1.3 1.3 1.3 1.3 additive package ⁸ Irganox L 0.1 0.1 0.1 0.1 135⁹Infineum 0 0 0.25 0.25 P655¹⁰ HVI 160B¹¹ 44 44 44 0 HVI 60¹² 54.6 0 0 0GTL 19¹³ 0 0 0 44 GTL 3¹⁴ 0 54.6 54.35 54.35 Total 100 100 100 100(weight %): JASO 81 82 86 98 Lubricity (M340-92) JASO Smoke 47 49 50 51Index (M342- 92) JASO Exhaust 52 71 81 203 Port Blocking Index (M343-92) Laboratory Tests: Vk 100° C. 6.98 5.05 5.05 6.98 (ASTM D-445 (mm²/s)Vk 40° C. 46.07 25.57 25.44 35.34 (ASTM D-445) (mm²/s) VI (ASTM D- 108127 128 163 2270)

-   -   8. 2-stroke performance additive package containing aminic        dispersant, antioxidants (mixed hindered phenols and aminic        antioxidants), over-based detergents from the range calcium        phenates and calcium salicylates    -   9. antioxidant commercially available from CIBA Speciality        Chemicals, Berne, Switzerland    -   10. Lubricity additive commercially available from Infinenum,        Milton Hill, Oxfordshire, UK    -   11. Mineral Group I base oil commercially available from Shell        Pernis Refinery, Rotterdam    -   12. Mineral Group I base oil commercially available from Shell        Pernis Refinery, Rotterdam    -   13. Fischer-Tropsch base stock having a kinematic viscosity at        100° C. of 19 cSt prepared according to the method of U.S. Pat.        No. 7,354,508.    -   14. Fischer-Tropsch base stock having a kinematic viscosity at        100° C. of 3 cSt prepared according to the method of U.S. Pat.        No. 7,354,508.

Example 5 and Comparative Examples C and D

2-stroke engine oil compositions were prepared having the formulationsset out in Table 3. The formulations were prepared by mixing theadditives with the base oils according to conventional preparationmethods. In order to determine the exhaust port blocking behaviour the 2stroke engine oil compositions were subject to the Exhaust Port BlockingTest Method JASO 343-92. The results are shown in Table 3 below.

TABLE 3 Comparative Comparative Example C Example 5 Example D 2 stroke25 25 25 solvent¹⁵ Polybutylene¹⁶ 25 25 25 HVI 65¹⁷ 27.96 33.88 32.40HVI 650¹⁸ 19.44 0 0 GTL 19¹⁹ 0 13.52 0 Flavex 595²⁰ 0 0 15 Additive 2.52.5 2.5 Package²¹ Irganox L 135²² 0.1 0.1 0.1 Total (weight %) 100 100100 Physical Data: kV 40° C. 40 33.05 38.03 kV 100° C. 7.256 6.558 6.815Density at 15° C. 860 849.3 869 (Kg/m₃) Pour Point/° C. −39 −33 −33Flashpoint/° C. 83 84 83 Results (JASO- 343-92): JASO M 343-92 100 24369 Port Blocking Index

-   -   15. 2 stroke solvent ShellSol D70B solvent, commercially        available from Shell Chemicals, The Netherlands    -   16. Polybutylene having a molecular weight of 950    -   17. Mineral API Group I base oil commercially available from        Shell Pernis Refinery, Rotterdam    -   18. brightstock commercially available from Shell Pernis        Refinery, Rotterdam    -   19. Heavy Fischer-Tropsch base stock having a kinematic        viscosity at 100° C. of 19 cSt.    -   20. A (brightstock) residual aromatic extract commercially        available from Shell Pernis Refinery, Netherlands    -   21. 2-stroke performance additive package containing aminic        dispersant, antioxidants (mixed hindered phenols and aminic        antioxidants), over-based detergents from the range calcium        phenates and calcium salicylates    -   22. antioxidant commercially available from CIBA Speciality        Chemicals, Berne, Switzerland

Discussion

The examples show that a heavy residual GTL base oil (19 cSt kinematicviscosity at 100° C.) in combination with polybutylene (PB) gives abetter port blocking performance than a formulation containing solely PBas heavy base stock component, which demonstrates that heavy residualGTL base oil is an effective partial polybutylene replacement. InExample 1 the major change in the formulation compared to ComparativeExample A was to reduce PB and replace with a heavy residual GTL baseoil. A minor modification was made to the API Gp I high viscosity index(HVI) base stock to maintain iso-viscometrics.

In Comparative Example B and Examples 2 to 4, it can be seen that alight GTL base oil (GTL-3) gives an improvement in port blockingperformance compared to an all mineral (API Gp I) analogue formulation.Further, the Example 4 shows that use of the combination of light andheavy Fischer-Tropsch base oils, light Fischer-Tropsch base oil GTL-3together with heavy Fischer-Tropsch base oil GTL-19, gives anexceptional improvement in port blocking performance compared to thestandard (API Gp I) mineral oil based formulation under iso-viscousconditions. Examples 2 to 4 are all 2 stroke oil formulations containingno PB, and yet suitable port blocking behaviour is obtained.

In Comparative Examples C and D and Example 5, the standard 2 strokeengine oil formulation, which normally had a polybutylene content of 35wt %, was re-formulated to 25 wt % polybutylene in the formulationtogether with a replacement amount of a heavy base stock component. Itwas noted that there was an improvement in the port blocking propensityof the 2-stroke formulation, for a range of heavy base oils, in theorder GTL-19> brightstock (HVI-650)> residual aromatic extract (Flavex595).

1. A method comprising lubricating a 2-stroke engine with a lubricatingoil composition comprising at least one Fischer-Tropsch derived baseoil, wherein the lubricating oil composition provides reduced exhaustport blocking in the 2-stroke engine.
 2. The method of claim 1 whereinthe Fischer-Tropsch derived base oil has a kinematic viscosity at 100°C. in the range of from 2 mm²/s to 30 mm²/s.
 3. The method of claim 1wherein the Fischer-Tropsch derived base oil has a kinematic viscosityat 100° C. in the range of from 2 mm²/s to 10 mm²/s.
 4. The method ofclaim 3 wherein the Fischer-Tropsch derived base oil has a kinematicviscosity at 100° C. in the range of from 2 mm²/s to 4 mm²/s.
 5. Themethod of claim 1 wherein the Fischer-Tropsch derived base oil has akinematic viscosity at 100° C. in the range of from 12 mm²/s to 30mm²/s.
 6. The method of claim 5 wherein the Fischer-Tropsch derived baseoil has a kinematic viscosity at 100° C. in the range of from 18 mm²/sto 22 mm²/s.
 7. The method of claim 5 wherein the lubricating oilcomposition comprises less than 2 wt % of a Fischer-Tropsch derived baseoil having a kinematic viscosity at 100° C. in the range of from 2 mm²/sto 10 mm²/s.
 8. The method of claim 1 wherein the lubricatingcomposition comprises a first Fischer-Tropsch derived base oil having akinematic viscosity at 100° C. in the range of from 2 mm²/s to 10 mm²/sand a second Fischer-Tropsch derived base oil having a kinematicviscosity at 100° C. in the range of from 12 mm²/s to 30 mm²/s.
 9. Themethod of claim 8 wherein the weight ratio of the first Fischer-Tropschderived base oil and the second Fischer-Tropsch derived base oil is inthe range of from 10:1 to 1:5.
 10. The method of claim 1 wherein thelubricating oil composition comprises 5 wt % or greater of a hydrocarbonsolvent.
 11. The method of claim 1 wherein the lubricating oilcomposition additionally comprises a smoke suppression agent selectedfrom the group consisting of polybutene, polyisobutylene, and mixturesthereof.
 12. The method of claim 1 wherein the lubricating oilcomposition additionally comprises a detergent/dispersant additivepackage.
 13. The method of claim 1 wherein the lubricating compositionadditionally comprises a lubricity additive.
 14. A 2-stroke lubricatingengine oil composition comprising (i) at least one Fischer-Tropschderived base oil having a kinematic viscosity at 100° C. in the range offrom 2 to 30 mm²/s and (ii) 5 wt % or greater of a hydrocarbon solvent;wherein the lubricating engine oil composition has a Blocking Index ofgreater than 130 as measured by the JASO M343-92 Exhaust System BlockingTest Method.
 15. A 2-stroke lubricating engine oil compositioncomprising (i) a first Fischer-Tropsch derived base oil having akinematic viscosity at 100° C. in the range of from 2 mm²/s to 10 mm²/sand (ii) a second Fischer-Tropsch derived base oil having kinematicviscosity at 100° C. in the range of from 18 mm²/s to 30 mm²/s; whereinthe weight ratio of the first Fischer-Tropsch derived base oil to thesecond Fischer-Tropsch derived base oil is in the range of from 10:1 to1:5, and wherein the lubricating engine oil composition has a BlockingIndex of greater than 130 as measured by the JASO M343-92 Exhaust SystemBlocking Test Method.
 16. The method of claim 8 wherein the weight ratioof the first Fischer-Tropsch derived base oil and the secondFischer-Tropsch derived base oil is in the range of from 1.98:1 to0.01:1.
 17. The method of claim 1 wherein the lubricating engine oilcomposition has a Blocking Index of greater than 130 as measured by theJASO M343-92 Exhaust System Blocking Test Method.
 18. The 2-strokelubricating engine oil composition of claim 15 wherein the weight ratioof the first Fischer-Tropsch derived base oil and the secondFischer-Tropsch derived base oil is in the range of from 1.98:1 to0.01:1.